Mercury column sphygmomanometers have been used for about a century and considered as the gold standard for blood pressure measurement. The measurement principle is based on the gravity of mercury, and, therefore, is accurate, reliable, easy to use and economical. The only major problem is that mercury is one of the top three toxic elements on earth. The health and environmental risks associated with mercury are very high. Many countries in the world now ban or restrict the use of mercury in healthcare and consumer products.
People have been attempting to replace mercury column sphygmomanometers with non-toxic ones. One example is an aneroid sphygmomanometer that is based on the elastic deformation property of a metal. Aneroid sphygmomanometers have not gained wide acceptance for diagnosis of hypertension or high blood pressure due to the fact that they need regular calibration. Another example is an electronic automated sphygmomanometer that is based on an empirical method called an oscillometric technique. Automated sphygmomanometers have found acceptance for home use and hospital monitoring stations. However, they have not been widely accepted for medical diagnostic purposes in clinical offices due to their inaccuracy for certain patients and certain blood pressure ranges. Medical sphygmomanometers for the diagnosis of hypertension require high accuracy and reliability. The commonly accepted accuracy is 3 mm Hg in the range of 0-200 mm Hg and 2% of the reading in the range of 200-300 mm Hg.